The data of a logical volume (hereafter simply referred to as a volume in some cases) that is included in the storage system has been backed up conventionally. As the backup, a snapshot has been known for instance.
For a first method of a snapshot management, when a write access occurs for a volume of a save source (a primary volume), a storage system saves the data in a region of a write destination of a primary volume to a volume of a save destination (a secondary volume). After that, the storage system writes the data of a write target to the primary volume, and returns a response of a write completion to a write access source. For this method, a write response is deteriorated, that is, it takes a long period of time to return a response to the write access source from an occurrence of the write access occurs unfortunately.
On the other hand, a second method of a snapshot management, more specifically, the copy after write (CAW) technique has been known (see Patent Literature 1 for instance). For the copy after write (CAW) technique, in an occurrence of the write access, a storage system writes the data of a write target to a cache memory of the storage system and returns a response of a write completion to a write access source. After that (in an asynchronous manner with the write access), the storage system saves the data in a write destination region of a primary volume to a secondary volume, and writes the write target data in the cache memory to the primary volume. For the CAW technique, a write response is faster than that of the first method.